.buttonText {
  font: 18px/1.5 Helvetica, Arial, sans-serif;
}
a {
  color: white;
  text-decoration: none;
}

#button1 {
  background: #6292c2;
  border: 2px solid #eee;
  height: 28px;
  width: 90px;
  margin: 50px 0 0 50px;
  padding: 0 0 0 7px;
  overflow: hidden;
  display: block;
   
  /*Переход*/
  -webkit-transition: All 0.5s ease;
  -moz-transition: All 0.5s ease;
  -o-transition: All 0.5s ease;
  -ms-transition: All 0.5s ease;
  transition: All 0.5s ease;
   
  /*Скругленные углы*/
  -webkit-border-radius: 15px;
  -moz-border-radius: 15px;
  border-radius: 15px;
   
  /*Градиент*/
  background-image: -webkit-linear-gradient(top, rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.2));
  background-image: -moz-linear-gradient(top, rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.2));
  background-image: -o-linear-gradient(top, rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.2));
  background-image: -ms-linear-gradient(top, rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.2));
  background-image: linear-gradient(top, rgba(0, 0, 0, 0), rgba(0, 0, 0, 0.2));
}

#button1:hover {
  width: 250px;
}

<a href="$FILE_URL$" id="button1" class="buttonText"> Скачать   - Вес: $FILE_SIZE$</a>